The most common adrenal disease relates to excess mineralocorticoid production and is called primary aldosteronism (PA). Despite the common occurrence of PA (approximately 1 in 30 adults), little is known about its cellular origins. Recently, a set of somatic gene mutations that cause renin-independent aldosterone production were identified in adrenal adenomas. In vitro studies have confirmed that these mutations cause aldosterone production through effects on adrenal cell calcium homeostasis. This proposal will test the hypotheses: 1) that most adults have neoplastic cells bearing first hit somatic mutations that cause renin- independent aldosterone production; 2) PA results from the build up of these nests of cells or through additional multi-hit mutations that increase cell proliferatio, tumor development and excessive aldosterone synthesis. To test these hypotheses, two specific aims are proposed. Aim 1 will define the somatic mutations found in normal adrenals that exhibit adrenal aldosterone-producing cell clusters (APCC) and will test the hypothesis that APCC are dysplastic cells bearing somatic gene mutations that activate aldosterone production. Aim 2 will define the somatic gene mutations present in aldosterone-producing adenomas (APA) and test the hypothesis that APA share some mutations with APCC, but exhibit additional mutations that cause cell proliferation and tumor development. The impact of APCC and APA mutations on aldosterone production and cell proliferation will be determined using primary cultures of normal adrenal cells and the H295R adrenal cell line. Pharmacologic agents that inhibit aberrant mutation-stimulated aldosterone production will be defined. The proposed research will significantly improve our understanding of the mechanisms leading to mineralocorticoid excess and provide information needed for the future development of molecular diagnostics and targeted therapeutics to treat PA.